ymodem协议代码

以下是一个简单的 Ymodem 协议的示例代码，用于文件传输。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Ymodem 数据包的大小
#define PACKET_SIZE 128

// Ymodem 控制字符
#define SOH 0x01  // 数据头开始
#define STX 0x02  // 数据头开始（大包）
#define EOT 0x04  // 传输结束
#define ACK 0x06  // 确认接收
#define NAK 0x15  // 确认接收错误
#define CAN 0x18  // 取消传输

// Ymodem 数据包结构
typedef struct
{
    unsigned char soh_stx;  // 数据头标识（SOH-128字节数据包，STX-1024字节数据包）
    unsigned char seq;      // 包序号
    unsigned char nseq;     // 包序号的补码
    unsigned char data[PACKET_SIZE];  // 数据
    unsigned char crc1;     // CRC 字节 1
    unsigned char crc2;     // CRC 字节 2
} ymodem_packet;

// 计算 CRC16 校验和
unsigned short calc_crc16(const unsigned char *data, int size)
{
    unsigned short crc = 0;
    int i, j;
    for (i = 0; i < size; i++)
    {
        crc = crc ^ ((unsigned short)data[i] << 8);
        for (j = 0; j < 8; j++)
        {
            if (crc & 0x8000)
                crc = (crc << 1) ^ 0x1021;
            else
                crc = crc << 1;
        }
    }
    return crc;
}

// 发送一个数据包
int send_packet(FILE *file, unsigned char seq, unsigned char *buffer, int size)
{
    ymodem_packet packet;
    packet.soh_stx = (size == PACKET_SIZE) ? SOH : STX;
    packet.seq = seq;
    packet.nseq = ~seq;
    memcpy(packet.data, buffer, size);
    unsigned short crc = calc_crc16(buffer, size);
    packet.crc1 = (crc >> 8) & 0xFF;
    packet.crc2 = crc & 0xFF;
    fwrite(&packet, sizeof(ymodem_packet), 1, file);
    fflush(file);
    return size;
}

// 接收一个数据包
int receive_packet(FILE *file, unsigned char *buffer)
{
    ymodem_packet packet;
    fread(&packet, sizeof(ymodem_packet), 1, file);
    if (packet.soh_stx == EOT)
        return -1;  // 结束传输
    else if (packet.soh_stx == CAN)
        return -2;  // 取消传输
    else if (packet.soh_stx != SOH && packet.soh_stx != STX)
        return -3;  // 无效的包头
    else if (packet.seq != (packet.nseq ^ 0xFF))
        return -4;  // 包序号校验错误
    unsigned short crc = calc_crc16(packet.data, PACKET_SIZE);
    if (crc != ((packet.crc1 << 8) | packet.crc2))
        return -5;  // CRC 校验错误
    memcpy(buffer, packet.data, PACKET_SIZE);
    return PACKET_SIZE;
}

// Ymodem 发送文件
int ymodem_send(const char *filename)
{
    FILE *file = fopen(filename, "rb");
    if (file == NULL)
    {
        printf("Failed to open file: %s\n", filename);
        return -1;
    }
    fseek(file, 0, SEEK_END);
    long filesize = ftell(file);
    fseek(file, 0, SEEK_SET);

    unsigned char buffer[PACKET_SIZE];
    unsigned char seq = 0x01;
    int bytes_read = 0;
    int total_bytes_sent = 0;

    while (total_bytes_sent < filesize)
    {
        memset(buffer, 0x1A, sizeof(buffer));  // 填充数据区域
        bytes_read = fread(buffer, 1, PACKET_SIZE, file);
        if (bytes_read > 0)
        {
            send_packet(stdout, seq, buffer, bytes_read);
            total_bytes_sent += bytes_read;
            seq++;
        }
        else
        {
            printf("Failed to read file: %s\n", filename);
            fclose(file);
            return -1;
        }
    }

    // 发送结束包
    unsigned char eot = EOT;
    send_packet(stdout, seq, &eot, sizeof(eot));

    fclose(file);
    return 0;
}

// Ymodem 接收文件
int ymodem_receive(const char *filename)
{
    FILE *file = fopen(filename, "wb");
    if (file == NULL)
    {
        printf("Failed to create file: %s\n", filename);
        return -1;
    }

    unsigned char buffer[PACKET_SIZE];
    unsigned char seq = 0x01;
    int bytes_received = 0;

    while (1)
    {
        bytes_received = receive_packet(stdin, buffer);
        if (bytes_received > 0)
        {
            fwrite(buffer, 1, bytes_received, file);
            seq++;
            unsigned char ack = ACK;
            send_packet(stdout, ack, NULL, 0);
        }
        else if (bytes_received == -1)
        {
            printf("File transfer complete.\n");
            fclose(file);
            return 0;
        }
        else if (bytes_received == -2)
        {
            printf("File transfer canceled.\n");
            fclose(file);
            return 0;
        }
        else
        {
            printf("Error receiving packet: %d\n", bytes_received);
            fclose(file);
            return -1;
        }
    }
}

int main()
{
    // 使用示例：发送文件
    // ymodem_send("test.bin");

    // 使用示例：接收文件
    // ymodem_receive("received.bin");

    return 0;
}

这段代码实现了一个简单的 Ymodem 文件传输功能，包括发送和接收文件。你可以根据需要调用 `ymodem_send` 或 `ymodem_receive` 函数来执行相应操作。请注意，代码中的输入和输出使用的是标准输入输出流，你可能需要根据实际情况进行适当修改。